One common type of video system architecture includes a video encoder that provides a corresponding digital video signal to a digital-to-analog converter (DAC). The DAC converts the digital input signal to a corresponding analog signal format. Existing and future performance demands, such as can enable studio quality video, can require that the DAC should be at least 10-bit DAC and have linearity that is at least 50 dB. Performance requirements can also necessitate that the DAC operate at a relatively high clock rate, such as of up to 60 MHz or higher.
One challenge in designing a video amplifier is to provide a large output swing for the high-bandwidth video signal while also maintaining adequate linearity. Another consideration for the output buffer is matching the output impedance of the buffer with the load impedance. For example, impedance matching to the load (e.g. about 75Ω) is required to avoid reflections from the load at high frequencies such as are typically utilized in video frequencies. One common approach to achieve impedance matching is either by having a 75Ω in series with the load or by having 75Ω in parallel to the load. Each of these approaches, however, is not power and area efficient. For instance, these approaches typically require more external components than may be desirable in many applications.
The increasing demands of manufacturers to minimize cost while maintaining or improving performance have prompted significant design efforts and new manufacturing techniques. For example, many integrated circuits for video systems are being manufactured using ultra deep submicron processes. Circuits produced by such processes impose additional design considerations due to the requirement of low power consumption as well as substrate and supply rejection. The associated complexity of design and manufacture of such components is compounded in circumstances when having to design such a system with substantially zero-cost passive components (e.g., resistors and capacitors) in a base line CMOS process.